The present invention relates to an AC plasma display device and, in particular, to an electric circuit for use with the AC plasma display device.
FIG. 9 shows a conventional drive circuit for use with an AC plasma display panel of an AC plasma display device. The AC plasma display panel (hereinafter referred to as xe2x80x9cpanelxe2x80x9d as necessary), generally indicated by reference numeral 1, includes M data electrodes D1-m extending vertically and 2N pairs of sustain and scan electrodes, SUS1-2N and SCN1-2N, extending horizontally. The vertically extended data electrodes D1-m face to the horizontally extended sustain and scan electrodes, SUS1-2N and SCN1-2N, leaving a small space gap therebetween. The sustain and scan electrodes, SUS1-2N and SCN1-2N, are divided into two groups or blocks; the first group or block 2 including sustain and scan electrodes, SUS1-N and SCN1-N, and the second group or block 3 including sustain and scan electrodes, SUS(N+1)-2N and SCN(N+1)-2N.
The data electrodes D1-M are electrically connected with a data driver 4 having a pulse generator not shown for applying a drive signal or pulse voltage to each of the data electrodes D1-M. The sustain and scan electrodes, SUS1-N and SCN1-N, in the first group 2 are connected to sustain and scan drivers, 5 and 6, respectively. On the other hand, the sustain and scan electrodes, SUS(N+1)-2N and SCN(N+1)-2N, in the second group 3 are connected to sustain and scan drivers, 7 and 8, respectively.
The sustain drivers 5 and 7 include sustain/erase (S/E) pulse generators 9 and 10, respectively. Also, the S/E pulse generator 9 is electrically connected at its output through an output line 11 with each of the sustain electrodes SUS1-N so that the pulse generator 9 applies a certain signal or pulse voltage to each of the sustain electrodes SUS1-N. Likewise, the S/E pulse generator 10 is electrically connected at its output through an output line 12 with each of the sustain electrodes SUS(N+1)-2N so that the pulse generator 10 applies a certain signal or pulse voltage to each of the sustain electrodes SUS(N+1)-2N.
The scan driver 6 includes a scan/sustain (S/S) pulse generator 13 and switching circuit 14, and the scan driver 8 includes a S/S pulse generator 15 and switching circuit 16. The S/S pulse generator 13 is electrically connected at its output through an output line 17 with the switching circuit 14, which in turn connected with each of the scan electrodes SCN1-N. This allows the pulse generator 13 to apply a certain signal or pulse voltage to each of the scan electrodes SCN1-N. Likewise, the S/S pulse generator 15 is electrically connected at its output through an output line 18 with the switching circuit 16, which in turn connected with each of the scan electrodes SCN(N+1)-2N. This allows the pulse generator 15 to apply a certain signal or pulse voltage to each of the scan electrodes SCN(N+1)-2N.
In operation of the AC plasma display panel so constructed, the data, sustain and scan electrodes are applied with respective pulses. A process for displaying an instant image in the panel includes three steps or periods; writing, sustaining and erasing periods. In the first writing period or step, the predetermined writing pulse or signal is sequentially applied to each of the scan electrodes SCN1-2N, during which another predetermined pulse voltage or signal is applied to selected one or more of the data electrodes D1-M, according to the image to be displayed. This induces an electric discharge at discharge cells or pixel cells formed adjacent to intersections of the scan and data electrodes and corresponding to the selected data electrodes.
In the next sustaining period, the sustain electrodes SUS1-2N are applied with the predetermined sustain pulse voltage or signal, thereby sustaining the discharge at each of the selected discharge cells or image pixels according to the display data.
Finally, in the last erasing period, the predetermined erase pulse voltage or signal is applied to the sustain electrodes SUS1-2N to erase the residual electric discharge.
In the writing period, the switching circuits 14 and 16 switch the pulse voltages transmitted from the S/S pulse generators 13 and 15, respectively, so that the scan electrodes SCN1-N and SCN(N+1)-2N are applied with the predetermined pulse voltage in sequential order. Likewise, in the sustaining period, the predetermined pulse voltage transmitted from the S/S pulse generators 13 and 15 are applied to respective scan electrodes SCN1-N and SCN(N+1)-2N.
In the meantime, as best shown in FIG. 10, the conventional S/E pulse generators 9 and 10, S/S pulse generators 13 and 15, and the switching circuits 14 and 16 are mainly constructed with push-pull circuit of Field-Effect Transistors (FETs), for example. It should be noted that, for example, where a push-pull circuit is made of two FETs, X1 and X2, it is indicated as xe2x80x9cpush-pull circuit X1/X2xe2x80x9d hereinafter.
With the arrangement shown in FIG. 10, in the sustaining period, when FET(Q2) is kept off, the push-pull circuit Q1/Q3 switches FET(Q1) and FET(Q3) alternately. Also, when the FET(Sa1-N) are turned on, FET(Sb1-N) off, and FET(T3) off, the push-pull circuit T1/T2 switches FET(T1) and FET(T2) alternately, with a certain phase opposite to that of the push-pull circuit Q1/Q3. This allows a pulse voltage of xe2x88x92Vm volts to be applied to the sustain electrodes SCN1-N and scan electrodes SCN1-N alternately. Also, the sustain pulse voltage is applied to the sustain electrodes SUS(N+1)-2N in the same timing as the sustain electrodes SUS1-N, and to the scan electrodes SCN(N+1)-2N in the same timing as the SCN1-N.
In FIG. 9, suppose that a load for sustaining the discharge in a first region corresponding to the group 2 (upper half) is equal to that for sustaining the discharge in a second region corresponding to the group 3 (lower half). In other words, assume that an image is displayed in the whole area of the panel with a constant brightness. In this instance, an electric current flowing from the sustain electrodes SUS1-N to the S/E pulse generator 9 is equal to another electric current flowing from the sustain electrodes SUS(N+1)-2N to the S/E pulse generator 10 (i.e., Iua=Iub), and an electric current flowing from the scan electrodes SCN1-N to the S/S pulse generator 13 is equal to another electric current flowing from the scan electrodes SCN(N+1)-2N to the S/S pulse generator 15 (i.e., Ica=Icb).
It should be noted that the actual driver circuit includes resistance of lines and electric elements such as FETs. Therefor, the driver circuit is designed so that resistance from the power supply of xe2x88x92Vm volts for the S/E pulse generator 9 to the sustain electrodes SUS1-N is equal to that from the power supply for the S/E pulse generator 10 to the sustain electrodes SUS and a resistance from the power supply of xe2x88x92Vm volts for the S/S pulse generator 13 to the scan electrodes SCN1-N is equal to that from the power supply for the S/S pulse generator 15 to the scan electrodes SCN(N+1)-2N.
However, when displaying an image having its major part positioned in the first region (upper half) and its minor part positioned in the second region (lower half) with a constant brightness in its entire image area as shown in FIG. 11, in the sustaining period, the load for sustaining the discharge in the first region becomes greater than that in the second region. Therefore, the discharge current Iua flowing from the sustain electrodes SUS1-N to the S/E pulse generator 9 and the discharge current Ica flowing from the SCN1-N to the S/S pulse generator 13 become greater than the discharge current Iub from the sustain electrodes SUS(N+1)-2N to the S/E pulse generator 10 and the discharge current Icb from the SCN(N+1)-2N to the S/S pulse generator 15, respectively. This in turn results in that a voltage drop from the power source of xe2x88x92Vm volts for the S/E pulse generator 9 and S/S pulse generator 13 to the sustain electrodes SUS1-N and scan electrodes SCN1-N becomes greater than that from the power source for the S/E pulse generator 10 and S/S pulse generator 15 to the sustain electrodes SUS(N+1)-2N and scan electrodes SCN(N+1)-2N. Then, an effective pulse voltage applied to the sustain electrodes SUS1-N and scan electrodes SCN1-N becomes lower than that to the sustain electrodes SUS(N+1)-2N and scan electrodes SCN(Nxe2x88x92)-2N, respectively, which further results in that an intensity of the sustaining discharge between the sustain electrodes SUS1-N and scan electrodes SCN1-N becomes lower than that between SUS(N+1)-2N and SCN(N+1)-2N. This lowers the brightness in the first area of the group 2 than that in the second area of the group 3, leading to an unevenness of the brightness in the displayed image.
Accordingly, an object of the present invention is to provide an AC plasma display device capable of displaying an image with an even brightness, and another object of the present invention is to provide an electric circuit for preferably use in the AC plasma display device.
An AC plasma display device of the present invention includes a pair of spaced apart first and second plates. The first plate bears a plurality of electrodes each extending in a first direction, and the second plate bears a plurality of paired first and second electrodes each extending in another direction perpendicular to the first direction. The paired first and second electrodes are divided into a plurality of groups.
Further, the device includes a plurality of first connecting lines. Each of the first connecting lines is associated with the first electrodes in one of the plurality of groups, and the first connecting lines are connected to each other. Also provided are a plurality of second connecting lines. Each of the second connecting lines is associated with the second electrodes in one of the plurality of groups, and the second connecting lines are connected to each other.
In addition, the device includes a plurality of first pulse generators. Each of the first pulse generators is associated with one of the first connecting lines. Also provided are a plurality of second pulse generators. Each of the second pulse generators is associated with one of the second connecting lines.
In another aspect of the present invention, each of the first electrodes in each of the groups is extended out on one side of the plate and each of the second electrodes in each of the groups is extended out on the opposite side of the plate.
In another aspect of the present invention, the first electrodes in one of the plurality of groups are extended out on one side of the plate, and the first electrodes in another of the plurality of groups are extended out on the opposite side of the plate. Also, the second electrodes in the one of the plurality of groups are extended out on the opposite side of the plate, and the second electrodes in the another of the plurality of groups are extended out on the one side of the plate.
In another aspect of the present invention, the device further includes a plurality of first and second circuit boards. Each of the first circuit boards supports one of the first pulse generators. Also, each of the second circuit boards supports one of the second pulse generators.
Also, another AC plasma display panel has a display having first and second display regions and a plurality pairs of sustaining and scanning electrodes. The plurality of pairs are divided into first and second groups so that the first and second groups are assigned to the first and second display regions, respectively. Further provided are a sustaining electrode driver for driving the sustaining electrodes and a scanning electrode driver for driving the scanning electrodes. In addition, means is provided for providing the first and second display regions with the same brightness even if the first region is greater or smaller in size than the second region.